The present invention relates to an inkjet head and to a method of manufacturing the inkjet head, and in particular to an inkjet head wherein speed distribution of each channel is easily uniformed even incase of a harmonica type head chip, and to a method of manufacturing the inkjet head thereof.
In recent years, in inkjet heads to record images by jetting ink from a nozzle, multi channel has been developed to improve recording speed and image quality. In such multi channel inkjet head, uniformity of speed distribution of ink jetted from the nozzles is an important factor. Since jetting speed of ink from the nozzle is related to a volume of ink particle and a diameter of ink particle, the channel characteristics including above factors have to be uniformized.
In inkjet head, there are a type wherein the inkjet head moves relative to a recording sheet and the other type wherein recording sheet moves relative to the stable inkjet head. In both types, nonuniform channel characteristics cause dispersion of landing accuracy of ink due to nonuniform speed distribution, thus deteriorates the quality of obtained image. Inkjet head in practice usually has some speed distribution because of dispersion of performance of PZT as a material and of non-uniformity of production process.
To make speed distribution uniform, there is a method to optimize driving voltage for each channel, however since a driving circuit has to be provided for each channel, cost increase is a problem. Usually, because a single power source applies voltage to each channel, each driving voltage becomes the same and it is unavoidable that speed of ink jetted from each nozzle varies.
Conventionally, technologies to make the speed distribution uniform have been known. They are a technology to configure the head using piezoelectric oscillator wherein a part of electrode is removed to obtain desired electro-mechanical characteristics (Patent document 1), a technology to trim an electrode surface of piezoelectric element so that characteristic variation among each nozzle is minimized by checking jetting characteristics of ink through a characteristic measuring device after assembling the head (Patent Document 2), and a technology to adjust ink speed by providing a cutout section in a common electrode of piezoelectric surface of piezoelectric element where distortion due to unimolf mode occurs when variations are measured among each nozzle through measurement of ink speed from each nozzle (patent Document 3). However, it is preferred that speed distribution is obtained by actual driving and the electrode is adjusted by trimming based on the result of speed distribution.
Meanwhile, among inkjet heads, there is known an shearing mode inkjet head in which channels are formed by grinding, driving electrodes are formed on the driving walls separating each channel, and dogleg shear distortion is caused by applying voltage to the driving electrode so as to jet ink in the channel from the nozzle.
Among them, an inkjet head (for example Patent document 4 and 5) wherein an actuator to jet ink is configured by so-called harmonica type head chip in which the driving wall composed of piezoelectric element and the channel are arranged alongside alternatively, and an outlet port and an inlet port of the channel are provided each on a front and rear surfaces, can be produced from one substrate in a large number at one time with extremely high productivity. Also, due to its straight shape through out the inlet port to the outlet port of the channel, it has merits of good air purging ability, high electric power efficiency, low heat generation and high speed response. In the inkjet head having such harmonica type head chip, ability of recording higher quality image is also desired by making speed distribution among each nozzle uniform.
In such harmonica type head chip, connection of a wiring to apply driving voltage to the driving electrode is difficult. Then, usually, the electrode to be connected with each driving electrode is extended to outside the head chip and a wiring is connected outside the head chip.
For example, in the technology mentioned in Patent Document 4, the head chip is placed between two substrata and the electrode is formed to be connected with each driving electrode electrically on the substrata so that driving voltage from the driving circuit is applied to each electrode through the substrata. In this case, an ink supply channel is formed by arranging a wall section across two substrata on rear surface (inlet port side of the channel) of the head chip.
Also, in a technology mentioned in Patent Document 5, the head chip is placed between two substrata, an ink supply chamber is formed by providing a wall section across two substrata on the rear surface (inlet port side of the channel) of the head chip, the wall section further protrudes backward from the substrata, and the electrode to be electrically connected with each driving electrode is formed on the substrata so that driving voltage is applied from the driving circuit to each driving electrode by using the substrate and the protruding section.    Patent document 1: Tokkaishou 57-181874    Patent document 2: Tokkaishou 61-118261    Patent document 3: Tokkai 2000-127384    Patent document 4: Tokkai 2004-209796    Patent document 5: Tokkai 2004-358751
In case of inkjet head having harmonica type chip head, as disclosed in Patent document 4 and 5, the driving electrode is completely closed in the channel. Also, on the rear surface side of the head chip, there is located a substrate where the electrode to apply driving voltage to each driving electrode is extended. Thus, it is difficult to adjust the driving electrode by trimming after manufacturing the inkjet head because the substrate obstructs adjustment.
If flexible material such as FPC (flexile printed circuit) is use for each substrate, it is possible to bend the substrate in a large angle to trim each driving electrode. However, bending status has to be kept during trimming work and it is not preferable since there are risks of folding down, separation and breakage of the substrate.